RSC-4128
Data Sheet
34
P/N 80-0206-R
© 2006 Sensory Inc.
Each comparator has two analog inputs, designated “+” and
“-“, and one digital output. When the analog voltage on the
“+” input is greater than the analog voltage on the “-“ input,
the digital output is a high level. This is indicated by a “1” in
the “cmpCtl” register (register D4) Bits 7 & 6 for Comparators
A and B, respectively. When the analog voltage on the “+”
input is less than the analog voltage on the “-“ input, the
digital output is a low level. This is indicated by a “0” in the
“cmpCtl” register (register D4) Bits 7 & 6 for Comparators A
and B, respectively. Bits 7 and 6 are the comparator outputs
and are “Read-Only” by the processor.
Each comparator can be separately enabled or disabled.
When a comparator is disabled, both inputs are isolated from
any circuitry common to both comparators, the inputs are
grounded, and the comparator power is turned off.
Comparator Multiplexing
Each comparator “+” input has an analog multiplexer that
selects between one of two external signals. When Bit3 of
“cmpCtl” is programmed to “0”, comparator input A+ is
multiplexed to P2.0 and input B+ is multiplexed to P2.1.
When Bit3 of “cmpCtl” is programmed to “1”, comparator
input A+ is multiplexed to P2.3 and input B+ is multiplexed to
P2.4.
The “-“ inputs of both comparators are connected
together. This common “-“ input can be multiplexed to either
an external comparator reference signal input through P2.2,
or the Comparator Reference Voltage (CRV).
Comparator Reference Voltage
The internal Comparator Reference Voltage (CRV) is derived from a multi-tap resistive divider and a 4-bit analog
multiplexer. Register “cmpRef” controls the Comparator Reference Voltage. The power for the Comparator
Reference Voltage is provided by unregulated Vdd. This means that the CRV will track external voltages referenced
from the system supply, giving consistent comparisons as the system supply drops. Power to the CRV is gated by
decoding the comparator configuration. The voltage select value in “cmpRef” Bits[3:0] selects one of 16 outputs of
an analog multiplexer connected to 16 equally spaced taps. The Comparator Reference Voltage covers the range
from 0.15*Vdd to 0.90*Vdd in steps of 0.05*Vdd and is given by 0.15*Vdd + (D3[3:0]/20)*Vdd.
In some configurations the Comparator Control register can be set up once and simply read thereafter. In many
configurations it will be necessary to switch the input multiplexers and/or re-program the reference voltage
repeatedly. These multiplexing and selection operations will have settling times of approximately 10 microseconds.
When the “pdn” bit is set for Idle or Sleep mode the entire comparator unit is powered down, but the contents of the
“cmpCtl” and “cmpRef” registers are preserved. When the RSC-4128 wakes up the comparators resume normal
operation.
A
A P2.0
A P2.3
B
A P2.1
A P2.4
A P2.2
CmpCtl=010
A
A P2.0
A P2.3
B
D P2.1
D P2.4
A P2.2
OFF
CmpCtl=100
A
A P2.0
A P2.3
B
A P2.1
A P2.4
D P2.2
iVREF
CmpCtl=001
A
D P2.0
D P2.3
OFF
B
A P2.1
A P2.4
A P2.2
CmpCtl=110
CmpCtl=101
A
D P2.0
D P2.3
OFF
B
A P2.1
A P2.4
D P2.2
iVREF
A
A P2.0
A P2.3
B
D P2.1
D P2.4
D P2.2
iVREF
OFF
CmpCtl=011
A
A P2.0
A P2.3
B
A P2.1
A P2.4
OFF
OFF
A P2.2
CmpCtl=000
A
D P2.0
D P2.3
B
D P2.1
D P2.4
OFF
OFF
D P2.2
CmpCtl=111
RSC-4128 Comparator Unit
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